The field of art to which this invention pertains is catalysts for the hydrogenation of organic compounds.
Fatty alcohols, i.e., aliphatic, predominantly linear, primary alcohols with chain lengths of more than 8 carbon atoms, are important intermediates in the chemical industry. They are used by preference to produce tensides such as fatty alcohol sulfates, polyglycol ethers or polyglycol ether sulfates.
Fatty acids or fatty acid esters, such as the mixture of different chain lengths found in natural fats and oils, are important raw materials for the production of fatty alcohols. They are converted to fatty alcohols by catalytic hydrogenation under pressure, wherein copper-chromium catalysts have proven to be particularly effective.
The hydrogenation reaction is carried out as a suspension hydrogenation, as a gas phase hydrogenation, or in the trickling [liquid] phase. Sufficiently high reaction rates are reached only at pressures about 250 bar and temperatures in the range of 260.degree. to 300.degree. C. As a general rule, the triglycerides are transesterified with methanol by known methods before the hydrogenation, and free fatty acids are esterified. Nevertheless, the reaction mixture has a residual concentration of free carboxylic acids.
The esterifying suspension hydrogenation by the Lurgi process is one important industrial example. In this process, the fatty acid mixture is introduced continuously into the hydrogenation reactor and esterified in situ with the fatty alcohol which is present in excess.
The presence of the free fatty acids obviously places high demands on the resistance of the catalysts to oxygen. Attack by the acids can wash out the catalyst metals, particularly copper, so that the effectiveness of the catalyst is degraded. Furthermore, the product is contaminated by metal soaps, or copper-containing materials deposit in the hydrogenation reactor in the subsequent parts of the plant.
The Cu--Cr oxide catalysts currently used have satisfactory hydrogenation activity and adequate resistance to the fatty acids in the reaction mixture. One major disadvantage of these catalysts, though, is their chemical composition. Like all catalysts, they lose their activity with time and must be disposed of. Used chromium-containing catalysts are considered environmentally hazardous substances, especially since a content of hexavalent chromium cannot be ruled out. Disposal is an increasing problem for operators of fatty alcohol plants, and the costs of disposal affect the economy of the process.
Also, in hydrogenation of aldehydes and ketones a certain content of acidic components can impair the catalyst properties.
Catalysts for hydrogenation of oxygen-containing compounds such as carboxylic acid esters in the vapor phase are known from EP A-0434062. Their major components are copper oxide and aluminum oxide, along with zirconium oxide. The oxide precursors of these catalysts are calcined at not more than 500.degree. C., so that their acid resistance is low. The activity of the catalysts is also relatively low.
A catalyst for reaction of carbon oxides with water vapor is known from SU-A-39 90 97. It contains copper oxide, zinc oxide and aluminum oxide. No zinc oxide is needed for catalysts used in hydrogenation of higher organic compounds which contain the carbonyl function.
A catalyst based on copper oxide and oxides of trivalent metals for reaction of carbon monoxide with hydrogen is known from SU A-38 22 61. Possible trivalent metals are aluminum, chromium, manganese and iron. Chromium is an essential component of these catalysts.
A process for production of hydrogen by reaction of carbon monoxide or carbon monoxide-containing gases with hydrogen at elevated temperatures is known from German B-1 248 623. The process employs catalysts based on copper oxide, aluminum oxide and/or chromium oxide and/or manganese oxide. In all the examples, the catalysts contain chromium oxide. The process has no points in common with the process for which the catalysts of this invention are to be used.
A procedure for producing an oxidation catalyst is known from DD A-242 183. The catalyst precursor is made from copper nitrate, manganese nitrate and aluminum nitrate by precipitation with aqueous sodium carbonate solution. The precursor is washed, dried, and ignited. The aluminum oxide content of these catalysts is greater than 70% by weight.
Hydrogenation catalysts based on copper, aluminum, and a metal from the group consisting of magnesium, zinc, titanium, zirconium, tin, nickel, cobalt, or mixtures of them are known from EP A-0 434062. The catalysts contain no manganese.
A process for production of alcohols using copper-zirconium oxide catalysts is known from German A-4 021 230. These catalysts contain no manganese or aluminum.
Copper-manganese catalysts for hydrogenation of fatty acids, fatty acid glyceride esters or the lower alkyl esters of fatty acids to fatty alcohols of corresponding chain length are known from German A-4 028 295. These catalysts contain no aluminum.
The objective of the present invention is to obtain catalysts having high hydrogenating activity, good resistance to acidic components and, at the same time, no environmentally damaging effect. Such catalysts are to be used for hydrogenating organic compounds, particularly compounds containing the carbonyl function, such as aldehydes, ketones, or carboxylic acids or their esters.